Mix the cheeses and sour cream in a bowl; add chilies and stir. Set aside.
Heat 2 tsp. butter in skillet over medium heat. Add tortilla and sprinkle on thin layer of cheese mixture to cover surface. Fry 30 seconds, fold tortilla over into half circle to form quesadilla. Continue cooking, turning often til cheese is melted and tortilla is golden brown.
Repeat with each tortilla. Keep cooked quesadillas warm while other are prepared. Cut each quesadilla into 3 wedge shaped pieces, serve with salsa and eat while warm.